A CMOS analog front end circuit for an FDM-based ADSL system

To cope with the high attenuation and the large echo return of copper telephone wire, the analog front end must feature low-noise enhancement, accurate channel filtering and high dynamic range. Two 14th-order continuous-time bandpass filters with on-chip automatic tuning provide the required channel separation in a narrow transition band (i.e. 96 kHz-138 kHz). A Gm-C integrator achieve over 60dB linearity of these filters. By using 4th-order /spl Sigma//spl Delta/ ADC and 6th order /spl Sigma//spl Delta/ DAC architectures, 12 b data conversion accuracy is achieved at 1.54 MHz Nyquist rate.